As methods for measuring a position of an object having a reflective surface in the three-dimensional space, inventions disclosed in Patent Documents 1 and 2 are known. According to the invention in Patent Document 1, an object having an illuminated reflective surface is captured by two cameras, and the direction of normal for the reflected light reflected by the object having the reflective surface is calculated based on the captured images. Next, according to the invention in Patent Document 1, corresponding pixels between the images are searched based on the direction of normal, and three-dimensional measurement (stereoscopic measurement) is carried out based on a parallax between the corresponding pixels. According to the invention in Patent Document 2, laser spot light is illuminated to an object having a reflective surface, and the light reflected from the object having the reflective surface is observed by two image sensors. Next, according to the invention in Patent Document 2, an incidence vector of the observed reflected light is calculated, and a position of the spot light on the object having the reflective surface is calculated based on the calculated incidence vector.
In addition, as methods for measuring a shape of an object having a mirror reflective surface, inventions disclosed in Patent Documents 3 and 4 are known.